The present invention relates to a handover between different networks (i.e., heterogeneous networks), discloses a broadband wireless access (BWA) system as an example of a variety of communication systems.
The broadband wireless access (BWA) system and a variety of messages for use in the broadband wireless access (BWA) system will hereinafter be described in detail.
The IEEE 802.16e system based on the international standardization of the broadband wireless access (BWA) system does not include a hierarchical structure (e.g., HLR, VLR, MSC, BSC, RNC), differently from conventional 2G and 3G mobile communication systems. The IEEE 802.16e system includes only a Mobile Subscriber Station (MSS), a Base Station (BS), and an Authentication Service Authorization (ASA). A physical layer (PHY) and a medium access control (MAC) layer are defined between the base station (BS) and the mobile subscriber station (MSS).
FIG. 1 is a structural diagram illustrating the frame of an OFDMA physical layer of the broadband wireless access (BWA) system.
A downlink (DL) sub-frame begins at a preamble used for synchronization and equalization at the physical layer, and includes a broadcast-type DL-MAP message for defining the location and usage of a burst assigned to a downlink (DL) and a UL-MAP message for defining the location and usage of a burst assigned to an uplink (UL), such that it defines an overall frame structure using the UL-MAP and DL-MAP messages.
An example of the DL-MAP message is shown in the following Table 1:
TABLE 1SyntaxSizeNotesDL-MAP Message Format( ){Management Message Type = 2 8 bitsPHY Synchronization FieldVariableSee appropriated PHYsepcificationDCD Count 8 bitsBase Station ID48 bitsBegin PHY Specific Section{See applicable PHY sectionFor(i=1;i<=n;i++){For each DL-MAPelement 1 to nDL-MAP_IE( )VariableSee corresponding PHYspecification}}If !(byte boundary)Padding Niddle48 bitsPadding to reach byteboundary}}
An example of the UL-MAP message is shown in the following Table 2:
TABLE 2SyntaxSizeNotesUL-MAP Message Format( ){Management Message Type=38 bitsUplink Channel ID8 bitsUCD Count8 bitsAllocation Start Time32 bits Begin PHY SpecificationSee application PHY sectionSection{for (i=1; i<=n;i++){For each UL-MAP element1 to n.UL-MAP_IE( )variableSee corresponding PHYspecification.}}if !(byte boundary){Padding Niddle4 bitsPadding to reach byte boundary.}}
The DL-MAP message defines usages assigned to individual bursts in a downlink interval of the burst-mode physical layer. The UL-MAP message defines the usages of the burst assigned to an uplink interval.
The information element (IE) for constructing the DL-MAP message distinguishes downlink traffic intervals at a user terminal by referring to a DIUC (Downlink Interval Usage Code), a CID (Connection ID), and burst location information (e.g., sub-channel offset, symbol offset, the number of sub-channels, and the number of symbols).
The information element (IE) for constructing the UL-MAP message defines its usage by an Uplink Interval Usage Code (UIUC) for each CID, and defines the location of a corresponding interval by duration information.
In this case, usages for each interval are determined according to UIUC values of the UL-MAP message. Each interval begins at a specific location spaced apart from the beginning point of a previous IE by a duration prescribed in the UL-MAP IE.
The Downlink Channel Description (DCD) message or the Uplink Channel Description (UCD) message is a MAC management message including UL/DL channel parameters of the base station (BS). The DCD or UCD message configured in the form of broadcast data is transmitted to mobile subscriber station (MSS) at intervals of a predetermined period.
The mobile subscriber stations (MSSs) acquire coding/modulation information of each burst from the DCD/UCD messages, and codes/decodes data according to the acquired coding/modulation information.
Each mobile subscriber station (MSS) receives the DCD and UCD messages periodically transmitted from the base station (BS), determines whether channel parameters of the base station (BS) are changed according to the received DCD and UCD messages, and updates the channel parameters according to the DCD/UCD messages.
The UCD message defines not only profile information associated with the coding/modulation scheme of the uplink burst, but also the set of CDMA codes associated with the ranging and band request operation. In addition, the UCD message further defines a back-off time required when an unexpected data collision occurs after the mobile subscriber station (MSS) transmits several codes.
The mobile subscriber station (MSS) compares a Configuration Change Count value with a DCD count value of the DL-MAP message. If it is determined that the Configuration Change Count value is different from the DCD count value of the DL-MAP message, the mobile subscriber station (MSS) determines that the DCD message has been changed to another value. Otherwise, if it is determined that the Configuration Change Count value is equal to the DCD count value of the DL-MAP message, the mobile subscriber station (MSS) determines that the DCD message is equal to a previously-received DCD message.
The DCD message is exemplarily shown in the following Table 3:
TABLE 3SyntaxSizeNotesDCD Message Format( ) {Management Message Type=1Downlink Channel IDConfiguration Change CountTLV Encoded information forthe overall channelBegin PHY SpecificationSection{For (I=1; I<=n;i++){Downlink Burst Profile  } }}
The TLV (Type, Length, Value) encoding information inserted into the above-mentioned DCD message is exemplarily shown in the following Table 4:
TABLE 4PHYNameTypeLengthValueScoreMIH5510 = MIH Capability not supportedA11Capability1 = MIH Capability supportedSupport
In the case of the OFDMA scheme of the broadband wireless access (BWA) system, the mobile subscriber station (MSS) generates a ranging request and an uplink band request using CDMA codes, such that it can adjust an uplink transmission parameter.
The base station configures the set of CDMA codes in the form of broadcast data, and transmits the broadcast-type CDMA codes to the mobile subscriber stations (MSSs). In this case, the set of CDMA codes are designed to generate the ranging and band requests using the uplink channel description (UCD) message.
The mobile subscriber station (MSS) selects a predetermined ranging code suitable for a desired usage from among CDMA codes acquired from the UCD message, and transmits the selected ranging code to the uplink interval assigned for the ranging process.
The UCD message is exemplarily shown in the following Table 5:
TABLE 5SyntaxSizeNotesUCD Message Format ( ){Management Message Type=08 bitsConfiguration Change Count8 bitsRanging Backoff Start8 bitsRanging Backoff End8 bitsRanging Backoff Start8 bitsRanging Backoff End8 bitsTVL Encoded information for the overall channelvariableBegin PHY Specific Section {TVL specificFor(i=1; i<=n;i++){For eachuplinkburst profile1 to n.Uplink_Burst_ProfilevariablePHY specific}}}
The mobile subscriber station (MSS) receives the DL-MAP and UL-MAP messages, and performs the ranging process for a network access procedure.
The present invention relates to a handover between heterogeneous networks, such that the handover technology between the heterogeneous networks will hereinafter be described in detail.
The IEEE 802.21, which is conducting the international standardization of the Media Independent Handover (MIH) between heterogeneous networks, provides a seamless handover and service continuity between the heterogeneous networks, resulting in greater convenience of a user. The basic requirements of the IEEE 802.21 are a MIH function, an event service (ES), and a command service (CS), and an information service.
The mobile subscriber station (MSS) acts as a multi-mode node for supporting at least one interface type, and the interface may be set to any one of the following types i), ii), and iii).
The type (i) indicates a wired-line format such as the 802.3-based Ethernet.
The type (ii) indicates a wireless interface based on the IEEE 802.XX, for example, the IEEE 802.11, the IEEE 802.15, and the IEEE 802.16.
The type iii) indicates an interface defined by the cellular standardization organization such as the 3GPP or 3GPP2.
As stated above, the present invention relates to a handover between heterogeneous networks, such that it supports a handover between various networks capable of providing a wired or wireless interface.
FIG. 2 is a circuit diagram illustrating a multi-mode mobile subscriber station (MSS). In this case, the multi-mode mobile subscriber station (MSS) is denoted by a multi-mode STA in the drawing.
Referring to FIG. 2, the multi-mode MSS includes a physical layer and a MAC layer for each node.
The MIH function of the mobile subscriber station (MSS) acting as a logical entity can interface with individual layers contained in a protocol stack via a service access point (SAP), and at the same time can be located at any location of the protocol stack.
The MIH (Media Independent Handover) must be defined between 802-based interfaces, or must be defined between the 802-based interface and the above-mentioned 802-based interface (i.e., 3GPP or 3GPP2). The mobility-supporting protocol (e.g., mobile IP or SIP (Session Initiation Protocol)) of upper layers must be supported to provide a handover service or seamless service.
The MIH function (MIHF) will hereinafter be described in detail.
The IEEE 802.21 standard can allow a variety of handover methods (e.g., “break before make” or “make before break”) to be easily operated.
The MIHF (Media Independent Handover Function) provides upper and lower layers with an asynchronous service and a synchronous service via the defined SAP (Service Access Point). For example, the asynchronous service is a Media Independent Event Service (MIES), and the synchronous service is a Media Independent Command Service (MICS).
The MIHF (Media Independent Handover Function) includes three MIHF services and a media independent handover protocol. The three MIHF services are a Media Independent Event Service (MIES), a Media Independent Command Service (MICS), and a Media Independent Information Service (MIIS).
The media independent event service will hereinafter be described in detail.
The media independent event service acts as information transmitted from a link layer to upper layers. The upper layers can receive the media independent event service information via a registration procedure.
In this case, in order to facilitate the handover by estimating the possibility of generating the handover, each upper layer including the mobility management protocol must receive link layer information indicating that the handover will be generated soon or the handover has just occurred.
The media independent event service can be classified into a link event and an MIH event. The link event begins at the entity of generating events of the lower layers below the 2-layer, and is generally terminated at the MIHF. The MIH event is propagated to upper layers over the S-layer, registered by the MIHF.
The link event or the MIH event can be classified into two types according to propagation areas.
If events are generated from the event source within the local stack, are transmitted to a local MIHF, or are transmitted from the MIHF to the upper layers in an uplink direction, the above-mentioned events are determined to be local events.
Otherwise, if the events are generated from the remote event source, are transmitted to the remote MIHF, and are then transmitted from the remote MIHF to the local MIHF, the above-mentioned events are determined to be remote events.
An example of the event service for the handover between heterogeneous networks will hereinafter be described in detail.
Link_Going_Down
The “Link_Going_Down” event occurs when the 2-layer connection will enter the “Link_Down” status within a specific time, and may be used as a signal for initializing the handover procedure.
The event source parameters (i.e., Local MAC and Remote MAC) are shown in the following Table 6:
TABLE 6NameTypeDestinationEventSourceEVENT_LAYER_TYPESource at which event is generatedEventDestinationEVENT_LAYER_TYPEDestination at which event is receivedMacMobileTerminalMAC addressMAC address of mobile subscriber station (MSS)MacOldAccessRouterMAC addressMAC address of previous access routerMacNewAccessRouterMAC addressMAC address of new access routerTimeIntervalTime in msecsTime at which link will enter “Link_Down”ConfidenceLevel%Level at which link willenter “Link_Down”UniqueEventIdentifierUsed if event rollback is generated
Link_Detected
The “Link_Detected” event indicates that a new specific link is in a Link-available status. The “Link_Detected” event indicates a possibility that a new base station (BS) or access point may provide the link quality better than that of a current base station (BS) or access point (i.e., a current connection point).
The event source parameters (i.e., Local MAC and Remote MAC) are shown in the following Table 7:
TABLE 7NameTypeDestinationEventSourceEVENT_LAYER_TYPESource at whichevent is generatedEventDestinationEVENT_LAYER_TYPEDestination atwhich event isreceivedMacMobileTerminalMAC addressMAC address ofmobile subscriberstation (MSS)MacNewAccessRouterMAC addressMAC addressof previous accessrouterMacOldAccessRouterMAC addressMAC address ofnew access router
Link_Parameters_Change
The “Link_Parameters_Change” event occurs when a variation of the link parameter value becomes higher than a specific limit level. The “Link_Parameters_Change” event may include a variety of link-layer parameters (e.g., the link speed, the Quality of Service (QoS), and the encryption value).
The event source parameters (i.e., Local MAC and Remote MAC) are shown in the following Table 8:
TABLE 8NameTypeDestinationEventSourceEVENT_LAYER_TYPESource at which event is generatedEventDestinationEVENT_LAYER_TYPEDestination at which event is receivedMacMobileTerminalMAC addressMAC address of mobile subscriber station(MSS)MacAccessRouterMAC addressMAC address of current access routerOldValueOfLinkParameterPrevious Value of Link pasrameterNewValueOfLinkParameterNew value of Link parameter
The media independent command service will hereinafter be described in detail.
The media independent command service determines link status information of the upper layers and link status information of other MIH users, and indicates commands for adjusting optimum operations of the multi-mode device. Also, the above-mentioned commands are transmitted to commands transmitted from upper layers over the 3-layer to lower layers below the 2-layer.
Similar to the above-mentioned media independent event services, the media independent command service is classified into a link command and a MIH command. The link command or the MIH command is classified into a local command and a remote command according to propagation areas. The local MIH command is generated from the upper layers, and is transmitted to the MIHF. For example, the MIHF may be indicative of an MIHF of an upper-layer mobility management protocol or another policy-engine MIHF.
The remote link commands are generated from the MIHF to adjust the lower-layer entities, such that the remote link commands are transmitted to the lower layers (e.g., MAC) or are transmitted from the MIHF to the physical layer (PHY).
The remote MIH command is generated from the upper layers, and is then transmitted to a remote equivalent stack. The remote link command is generated from the MIHF, and is then transmitted to lower layers of the remote equivalent stack.
The information service according to the present invention will hereinafter be described in detail.
The media independent information service (MIIS) provides a hierarchical network (i.e., a heterogeneous network) with a similar framework, such that the user can easily find or select a desired network from among a variety of networks. The MIIS can be accessed by all the networks.
The MIIS includes the following information elements:                Link access parameter        Security mechanism        Neighbor Map        Location        Provide and other Access Information        Cost of Link        
The MIH capability discovery message and its associated messages will hereinafter be described.
The “MIH_Capability_Discovery.request” message has the following characteristics.
The “MIH_Capability_Discovery.request” message does not include the MIH message payload. The type of the “MIH_Capability_Discovery.request” message is set to “1” using only the MIH header, such that the resultant message is transmitted to a destination. This message may be transmitted to the destination via the 2-layer (i.e., L2 layer) or the 3-layer (i.e., L3 layer).
If the entity for transmitting the above-mentioned “MIH_Capability_Discovery.request” message does not recognize the accurate address of a counterpart entity, and desires to recognize which one of entities within the network has the MIH function, the “MIH_Capability_Discovery.request” message is transmitted as a broadcast message.
Otherwise, although the entity for transmitting the “MIH_Capability_Discovery.request” message recognizes the address of the counterpart entity, and desires to recognize the presence or absence of the MIH function of the corresponding entity, the “MIH_Capability_Discovery.request” message is transmitted as a unicast message.
The “MIH_Capability_Discovery.response” message has the following characteristics.
If the entity for receiving the “MIH_Capability_Discovery.request” message has the MIH function, it answers the “MIH_Capability_Discovery.request” message using the “MIH_Capability_Discovery.response” message.
The “MIH_Capability_Discovery.response” message does not include the MIH message payload in the same manner as in the “MIH_Capability_Discovery.request” message, and the type of the “MIH_Capability_Discovery.response” message is set to “1” using only the MIH header, such that the resultant message is transmitted to a destination. In this case, the above-mentioned response message may also be transmitted via the L2 or L3 layer.
If the “MIH_Capability_Discovery.response” message is transmitted to a destination as described above, the destination address of the MIH header copies the source address of the “MIH_Capability_Discovery.request” message, and is filled with the duplicated source addresses, and the source address is filled with its own address.
The entity having the MIH function may periodically advertise its MIH function via the L2 or L3 layer.
A method for performing the handover between heterogeneous networks will hereinafter be described.
FIG. 3 is a flow chart illustrating a conventional handover procedure.
Referring to FIG. 3, if the multi-mode mobile subscriber station (MSS) is handed over from a wireless LAN access point to the broadband wireless access system, a method for acquiring MIHF performance information of the base station (BS) to which the multi-mode mobile subscriber station (MSS) will be handed over via the DCD message, and a network access procedure are depicted in FIG. 3.
As can be seen from FIG. 3, the MIH of the multi-mode mobile subscriber station (MSS) receives specific information from the link layer at step S301. This specific information indicates that a connection to a current access wireless LAN link will be released after the lapse of a predetermined time. In other words, the mobile subscriber station (MSS) receives a message indicating a release of the connection to a current access point (i.e., IEEE 802.11 of FIG. 3).
If the mobile subscriber station (MSS) recognizes the above-mentioned connection-release status, its MIHF transmits the “Link_going_down” primitive indicating that the connection will be remotely released at the MIH of the current access point at step S302. The above-mentioned “Link_going_down” primitive has been disclosed in Table 6, so that its detailed description will herein be omitted for the convenience of description.
The upper management entity of the mobile subscriber station (MSS) generates a command for scanning another link, such that it can be handed over from a current network to another network using the command. The above-mentioned command is transmitted to a corresponding interface link layer over the MIHF, and scans the actual link at step S303.
The broadband wireless access link scanned by the scan procedure S303 is transmitted to the MIHF via the “Link Detected” primitive at step S304. FIG. 3 shows a specific case in which a new access point is a wireless access link.
Upon receiving available link information, the MIHF or the upper management entity transmits the “Link Connect” command to the broadcast wireless access system link to establish a corresponding link at step S305.
The MAC layer of the base station (BS) broadcasts the DL-MAP and UL-MAP messages to the MAC layer of the mobile subscriber station (MSS) at each frame. Therefore, the mobile subscriber station (MSS) acquires the uplink- or downlink-frame structure, band allocation information, and DIUC and UIUC information, etc.
The MAC layer of the base station (BS) periodically transmits the DCD message including MIHF performance information of the base station (BS) to the mobile subscriber station (MSS). The mobile subscriber station (MSS) compares the DCD count value of the DL-MAP message with the configuration count change value of the DCD message. If it is determined that the DCD count value off the DL-MAP message is different from the configuration count change value of the DCD message, the mobile subscriber station (MSS) updates a current DCD message to a recently-received DCD message at step S307.
The MAC layer of the mobile subscriber station (MSS) transmits the MIHF performance information received by the DCD message to the MIHF or the upper management entity at step S308.
The base station (BS) broadcasts the UCD message including the uplink channel information along with the DCD message at step S309. However, it should be noted that the step S309 may occur prior to the step S308.
The step S309 may have the same operation period as in the step S307, and may transmit the recent UCD message content using the same method as in the step S307.
The mobile subscriber station (MSS) performs a specific process for connecting the L2 layer to the base station (BS) at step S310.
As can be seen from the above-mentioned steps S301˜S310, a conventional mobile subscriber station (MSS) is handed over from a current access point to a new access point. In other words, the conventional mobile subscriber station (MSS) performs the handover from the current access point to the new access point.
However, the above-mentioned conventional art has the following disadvantages.
If the mobile subscriber station (MSS) performs the handover from a current network to a new network according to the conventional art, it must access the new network, must wait for a broadcast message to be generated from the new network, and must receive the broadcast message from the new network, such that it can recognize system information required for connecting the new network.
In other words, after transmitting the “Link Connect” command for accessing the new network, the mobile subscriber station (MSS) receives control information broadcast from the new network, and finishes the handover procedure.
However, the mobile subscriber station (MSS) for attempting to perform the handover requires a delay time consumed for receiving a broadcast message from the new network, such that the handover may also be unavoidably delayed due to the delay time.